title: WW domain containing E3 ubiquitin protein ligase 1 (WWP1) negatively regulates TLR4-mediated TNF-α and IL-6 production by proteasomal degradation of TNF receptor associated factor 6 (TRAF6).
abstract: BACKGROUND
  Toll-like receptors (TLRs) play a pivotal role in the defense against invading pathogens by detecting pathogen-associated molecular patterns (PAMPs). TLR4 recognizes lipopolysaccharides (LPS) in the cell walls of Gram-negative bacteria, resulting in the induction and secretion of proinflammatory cytokines such as TNF-α and IL-6. The WW domain containing E3 ubiquitin protein ligase 1 (WWP1) regulates a variety of cellular biological processes. Here, we investigated whether WWP1 acts as an E3 ubiquitin ligase in TLR-mediated inflammation.
  
  
  RESULTS
  Knocking down WWP1 enhanced the TNF-α and IL-6 production induced by LPS, and over-expression of WWP1 inhibited the TNF-α and IL-6 production induced by LPS, but not by TNF-α. WWP1 also inhibited the IκB-α, NF-κB, and MAPK activation stimulated by LPS. Additionally, WWP1 could degrade TRAF6, but not IRAK1, in the proteasome pathway, and knocking down WWP1 reduced the LPS-induced K48-linked, but not K63-linked, polyubiquitination of endogenous TRAF6.
  
  
  CONCLUSIONS
  We identified WWP1 as an important negative regulator of TLR4-mediated TNF-α and IL-6 production. We also showed that WWP1 functions as an E3 ligase when cells are stimulated with LPS by binding to TRAF6 and promoting K48-linked polyubiquitination. This results in the proteasomal degradation of TRAF6.
authors.affiliation: Department of Pain Management, Provincial Hospital affiliated to Shandong University, Shandong University, Jinan, PR China.
authors.forename: Xiao-Wen
authors.initials: XW
authors.lastname: Lin
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Xu
authors.forename: Jian-Gang
authors.initials: JG
authors.lastname: Luo
authors.forename: Xue-Jiao
authors.initials: XJ
authors.lastname: Guo
authors.forename: Tao
authors.initials: T
authors.lastname: Sun
authors.forename: Xu-Li
authors.initials: XL
authors.lastname: Zhao
authors.forename: Zhi-Jian
authors.initials: ZJ
authors.lastname: Fu
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D055785:Gene Knockdown Techniques; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis*; D051379:Mice; D008810:Mice, Inbred C57BL; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D059748:Proteolysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000502:physiology*
chemical_list: D017931:DNA Primers; D015850:Interleukin-6; D048029:TNF Receptor-Associated Factor 6; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C510836:WWP1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex